RE: [ATM] Carbon Fiber for Spider Vanes

["Donald Good" <donald.good@comcast.net>]

Is the Home Depot foam advertised for use in fiber composite construction?
Or is it insulation foam?  When Shane says the resin might eat the foam,
read that as "dissolve".  Even when a particular foam is designed for use in
composites, there may be restrictions as to the resin system to be used.  In
addition to the eating problem, there may be bonding issues, too.

Did you prep the foam with a THIN coating of resin/microbead slurry?  This
is like a primer that seals the foam to prevent it from soaking up too much
resin from the fiber.  Kind of like a primer coat on wood.

When you say the cloth is held in place with Super 77, do you mean in spots
or a full coating?  The fiber in the pictures do not appear to be wetted out
with resin (transparency is wrong and too much weave texture is showing).
Is it post Super 77 and pre resin?  I also would check with the resin maker
as to compatibility, especially if it is a full coat.

I would also use 3 layers on the outside edges.  That will be a major
pressure surface.  Interleave the edge tabs with the side layers.  Use the
resin/microbead slurry to fill in spaces between the tabs and to feather the
edges for a smooth transition.  A technique for a smooth side is to apply
the sides without cutting out the holes.  After the layer dries, cut out the
hole smaller, and then use a router with flush cutting bit rated for
composites.  The outside edge can use the same router technique if the part
is placed wet side down on your release board with a little extra margin and
weighted from the foam side.

An important part that is missing is the mounting blocks.  These blocks can
be round hardwood inserts in the foam (2" diam x 1" for the foam thickness)
at the points that the bearings are attached to the rocker frame.  These
blocks and the foam are then covered with the side fiber layers and then
drilled for the frame attachment bolts.  They carry and distribute the load
from the frame to the bearings and the tightening load of the bolt, itself.
Do not expect the foam and fiberglass edges at a bolt hole to carry these
loads alone.  All such load points should be reinforced in a similar manner.
When drilling, use a bit rated for composites to reduce fraying.

WARNING, when drilling, routing, or cutting fiber parts, use proper
protection (eyes, skin, and breathing).

Clear skies,
Don

> -----Original Message-----
> From: atm-bounces@atmlist.net 
> [mailto:atm-bounces@atmlist.net] On Behalf Of Peter
> Sent: Wednesday, April 06, 2005 3:35 PM
> To: Dream - Telescopes & Accessories, Inc.; atm@atmlist.net
> Subject: RE: [ATM] Carbon Fiber for Spider Vanes
> 
> Shane,
> 
> Would you kindly provide me with an on list critique of the 
> making of my composite altitude bearings?
> 
> Brief Description:
> =================
> - Core material is polystyrene foam from Home Depot. 1" 
> thick. Very firm material.
> - Bearing surface has 2 layers of two direction woven fiberglass
> - Sides have 3 layers glass per side to provide the bearing stiffness
> - decorative inner forms are 1 layer glass
> - cloth held in place with Super 77 adhesive to maintain 
> position while the cloth wets out.
>   Trick I learned from model airplane makers.
> - laminate pressed between two waxed boards with 200lbs for 
> curing time
> - Transition temp of my epoxy Tg is 196 degrees F
> 
> Photos are: www.kitgear.com/atm/temp
> 
> The bearings turned out very nicely but I don't yet have 
> pictures of the completed parts. More to come...
> 
> Some questions I have are:
> =========================
> - What could I have done better but please understand that I 
> do not have vacuum bagging equipment?
> 
> - If I were to get vacuum bagging tools and materials then 
> would that technique work for complex parts like this?
> 
> - Should I worry about my epoxy Tg even if I paint my parts a 
> light color?
> 
> 
> Thanks in advance for any input you may share with us.
> 
> 
> Peter
> 
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